Humans spend a majority of their time in auditory environments that are complex and reverberant. An important and ongoing task for the auditory system is the segregation of target signals from interfering sounds and the suppression of echoes. The binaural system is known to be important in accomplishing these goals. The proposed research will investigate directional hearing in multi-source and reverberant acoustic environments. We will study sound localization, suppression of echoes, and speech intelligibility, in human adults with normal hearing, and with bilaterally-implanted cochlear implant users. Aim 1 will investigate the precedence effect (PE) using more everyday paradigms than those previously employed, with speech stimuli and multiple-echo patterns that vary in number, directional properties, intensity and spectral content. In Aim 2 we will investigate the impact of these echo patterns on speech intelligibility in the presence of competing sounds whose content and spatial locations and will be varied. We will test the hypothesis that "informational masking" can be induced when listeners experience uncertainty regarding the number, content and locations of competing sounds. In Aim 3 we will study binaural mechanisms in bilateral CI users through specialized hardware that controls the binaural synchronization between the two ears. Studies will measure localization, echo suppression, speech in intelligibility in complex acoustic environments, and basic binaural processes. This research addressed fundamental issues concerning the ability of humans to function in everyday listening situations. Problems in such environments are commonly reported by hearing impaired individuals. Studies in Aim 3 might contribute to the future design of hearing aids and cochlear implants that take advantage of binaural cues and compensate for the degradation of functioning in noisy and reverberant environments. [unreadable] [unreadable] [unreadable] [unreadable]